It is known that it is desirable to direct expression of a gene of interest ("GOI") in certain tissues of an organism--such as a plant. For example, it may be desirable to produce crop protein products with an optimised amino acid composition and so increase the nutritive value of the crop. It may even be desirable to use the crop to express non-plant genes such as genes for mammalian products. Examples of the latter products include interferons, insulin, blood factors and plasminogen activators.
However, whilst it may be desirable to achieve expression of a GOI in certain tissues it is sometimes important (if not necessary) to ensure that the GOI is not expressed in other tissues in such a manner that detrimental effects may occur. Moreover, it is important not to upset the normal metabolism of the organism to such an extent that detrimental effects occur. For example, a disturbance in the normal metabolism in a plant's leaf or root tip could lead to stunted growth of the plant.
CA-A-2006454 describes a DNA sequence of an expression cassette in which the potato tuber specific regulatory regions are localised. The expression cassette contains a patatin-gene with a patatin-gene promoter. The DNA sequence is transferred into a plant genome using agrobacteria. According to CA-A-2006454, the DNA sequence enables heterologous products to be prepared in crops.
One of the key plant enzymes is .alpha.-amylase. .alpha.-amylase participates in the pathway responsible for the breakdown of starch to reducing sugars in potato tubers. Genes coding for .alpha.-amylase in potato plants have been isolated and characterised. For example, see the teachings in EP-B-0470145.
In brief, .alpha.-amylase is encoded by a gene family consisting of at least 5 individual genes. Based on their homology the genes can be divided into two subfamilies--one of which is the type 3 amylase(s), the other of which is the type 1 amylase(s). The two groups of .alpha.-amylases are expressed differently, not only on the molecular level but also in different tissues of the potato plant.
In this regard, type 3 .alpha.-amylases are expressed in root, in tubers, in sprouts and in stem tissue; whereas type 1 .alpha.-amylases are expressed in sprout and stem tissues, but not in tubers.